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RT8206M Datasheet(PDF) 23 Page - Richtek Technology Corporation |
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RT8206M Datasheet(HTML) 23 Page - Richtek Technology Corporation |
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23 / 27 page  RT8206L/M 23 DS8206L/M-07 June 2012 www.richtek.com © Copyright 2012 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation. internal circuitry will be shut down during thermal shutdown. The RT8206L/M may trigger thermal shutdown if the LDO is not supplied from VOUTx, while input voltage on VIN and drawing current from the LDO are too high. Even if the LDO is supplied from VOUTx, overloading the LDO causes large power dissipation on automatic switches, which may result in thermal shutdown. Discharge Mode When standby or shutdown mode occurs, or the output under voltage fault latch is set, the output discharge mode is triggered. During discharge mode, the output capacitor will be discharged to GND through an internal 20 Ω switch. Shutdown Mode The RT8206L/M SMPS1, SMPS2 and LDO have independent enabling control. Drive ENLDO, EN1 and EN2 below the precise input falling edge trip level to place the RT8206L/M in its low power shutdown state. The RT8206L/M consumes only 20 μA of quiescent current while in shutdown. When shutdown mode is activated, the reference turns off. The accurate 1V falling-edge threshold on the ENLDO can be used to detect a specific analog voltage level and shutdown the device. Once in shutdown, the 1.6V rising edge threshold activates, providing sufficient hysteresis for most application. Power Up Sequencing and On/Off Controls (ENx) EN1 and EN2 control SMPS power-up sequencing. When the RT8206L/M applies in the single channel mode, EN1 or EN2 enables the respective outputs when ENx voltage rises above 2.5V, and disables the respective outputs when ENx voltage falls below 1.8V. Connecting one ENx to VCC and the other to REF will force the latter one's output to start only after the former one regulates. If both ENx are connected to REF, each output will wait for the regulation of the other one. However, in this situation, neither of the two ENx will be in regulation. OUTx FBx R1 V = V 1 R2 ⎡⎤ ⎛⎞ ×+ ⎜⎟ ⎢⎥ ⎝⎠ ⎣⎦ where VFBx is 2V (typ.). Output Inductor Selection The switching frequency (on-time) and operating point (% ripple or LIR) determine the inductor value as follows : ON IN OUT IR LOAD(MAX) t(V - V ) L = LI × × where LIR is the ratio of the peak-to-peak ripple current to the average inductor current. Find a low-loss inductor having the lowest possible DC resistance that fits in the allotted dimensions. Ferrite cores are often the best choice, because the powdered iron is inexpensive and can work well at 200kHz. The core must be large enough to prevent it from saturating at the peak inductor current (IPEAK) : IPEAK = ILOAD(MAX) + [(LIR / 2) x ILOAD(MAX)] This inductor ripple current also impacts transient-response performance, especially at low VIN − VOUTx differences. Low inductor values allow the inductor current to slew faster, replenishing charge removed from the output filter PHASEx LGATEx R1 R2 VOUTx VIN UGATEx VOUTx FBx GND Figure 6. Setting VOUTx with a Resistor-Divider Output Voltage Setting (FBx) Connect FB1 directly to GND or VCC for a fixed 5V output (VOUT1). Connect FB2 directly to GND or VCC for a fixed 3.3V output (VOUT2). The output voltage can also be adjusted from 2V to 5.5V with a resistor-divider network (Figure 6). The following equation is for adjusting the output voltage. Choose R2 to be approximately 10k Ω, and solve for R1 using the following equation : |
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